It is known to provide integrated circuits with multiple power domains. These power domains allow portions of the integrated circuit to be powered down (have their supply voltage removed) when they are not needed and so save energy. When this occurs, it is important that output signals being generated by a power domain which is being powered down and which are needed by another portion of the integrated circuit, or some other circuit operating in conjunction with the integrated circuit, should continue to be maintained in their original state. For example, between two power domains within an integrated circuit, one power domain may pass a particular bit value to another power domain(s) with that bit value being used to control processing in the other power domain. If the other power domain(s) can to continue processing, then this control signal should be maintained even though the first power domain is powered down.
One way of achieving the maintaining of output signals from the circuitry within a power domain (e.g. an area of core circuitry) which is being powered down is to surround that power domain with a wrapper of latch cells. Prior to the power domain being powered down, the output signals the circuitry within the power domain is generating can be transferred into the latch cells and then those latch cells can have power maintained to them during the power-down of the power domain which they surround. While such a technique does work, it suffers from the disadvantage that the action of the latch cells must be commanded and coordinated from a central controller. As an example, in the cycle prior to power-down of the domain, the latches must be supplied with an appropriate control and clock signal to move the output values into the latches. This adds complexity to the integrated circuit and its control during operation.